1. Field of the Invention
This invention relates to a charge condition adjusting apparatus, especially, the charge condition adjusting apparatus, which includes a voltage detecting device detecting each voltage between both electrodes (ends) of plural unit cells structured by connecting secondary batteries to each other; a discharging resistor for discharging the unit cell; and an equalizing device controlling discharge through the discharging resistor of the plural unit cells based on the voltages between the both ends of the respective unit cells detected by the voltage detecting device so as to equalize the voltages between both ends of the plural unit cells.
2. Description of the Related Art
A hybrid electric vehicle (HEV) driven together by an engine and an electric motor becomes popular. The HEV includes two types of batteries, which are a low-voltage battery of about 12V for starting the engine and a high-voltage battery for driving the electric motor. The high-voltage battery supplies a high voltage by connecting in series unit cells formed with secondary batteries, such as nickel-metal hydride batteries or lithium ion batteries.
By repeating to charge and discharge the high-voltage battery, respective voltages of both ends of the unit cells change to have various values, that is each charge condition (State-Of-Charge: SOC) is dispersed. For maintaining durability and safety of each unit cell, charging the unit cell may be prohibited when the highest SOC (largest voltage value between the both ends) of the unit cells reaches a presetted upper limit SOC (upper limit voltage value between the both ends), and discharging the unit cell may be prohibited when the lowest SOC (lowest voltage value between the both ends) of the unit cells reaches a presetted lower limit SOC (lower limit voltage value between the both ends).
Thereby, when the each unit cell has various SOC, a usable capacity of the battery is reduced actually. In the HEV, supplementing battery energy to a gasoline engine for hill-climbing, and regenerating energy back to the battery when go downhill, that is by assisting/regenerating, are not acted sufficiently, and actual power performance and fuel consumption ratio are reduced.
A discharge-type charge condition adjusting apparatus, which reduces dispersion of the voltage between the both ends of the each unit cell by detecting the voltages between the both ends of the plural unit cells, calculating an average voltage of the voltages between the both ends, connecting a unit cell, which has the voltage between the both ends larger than the average voltage, to a discharge resistor provided at each unit cell, and repeating to discharge charged capacity in the unit cell until the voltage between the both ends of the connected unit cell reaches the average voltage, is proposed in Patent Document 1. The Patent document 1 is JP2002-10511.